1. Technical Field
The present invention relates to an antitheft apparatus for an automotive vehicle for preventing the vehicle from being stolen, by use of an ID (identification) number allocated to each ignition key.
2. Description of the Related Art
An antitheft apparatus for an automotive vehicle has been known (Japanese Published Unexamined (Kokai) Patent Application No. 64-56253). In this antitheft apparatus, a transponder is buried at a head portion of an ignition key, and a specific ID number is stored in the transponder. When the ignition key is inserted into a key hole of a key cylinder and then rotated to a start position to drive an engine of the vehicle, the ID number (a predetermined code) is read from the ignition key and then collated with a plurality of ID numbers (codes) already registered in the antitheft apparatus. Here, if the ID number of the key now used has been already registered in the antitheft apparatus, the engine can be started. On the other hand, if not registered, the engine cannot be started for prevention of vehicle from being stolen.
On the other hand, when an engine of the automotive vehicle is being cranked to start the engine by passing current from a battery to a starter motor during cranking period, since a large starting current is passed from the battery to the starter motor and further the starting current is not constant, the battery voltage fluctuates violently, so that the battery voltage is not stable. Therefore, during the above-mentioned unstable cranking period, when an ID number is read from the transponder of the ignition key for collation with the ID numbers stored in the antitheft apparatus, there exists a problem in that an ID number communication error inevitably occurs, so that the antitheft apparatus operates erroneously.
To overcome this problem, conventionally the battery voltage applied to the starter motor (referred to as a cranking voltage, hereinafter) is monitored by an engine control unit to inhibit the ID number collation operation of the antitheft apparatus only during the cranking period. In this case, however, since the antitheft apparatus is inoperative during the cranking period, when the cranking period is prolonged intentionally by some method, the use of the ID number is ineffective.
Or else, there exists another antitheft apparatus such that the engine can be started with priority over the ID number collation operation. In this case, similarly, the antitheft characteristics are inevitably degraded.